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Solar heating not working as well as before

I have been using solar heating successfully for years, and installed new panels in late April last year after replacing original DE filter with a cartridge filter. Heating worked well all last summer and up until recently. But for the last month or so the water entering the pool is not as warm as previously (my wife says its tepid and she's right as usual). We have no thermometer in the line going from the pump to the pool (the solar heated water blasted it off scale once and it never recovered so I removed it). Air temperature the last couple of days was about 98-99 deg F. Today it is 97 deg and the pool temp is 82 and the water coming into the pool from the solar panels is at about the same temp. I "cleaned" the year-old filter cartridge today, and have been cleaning it about every two months with a cleaning wand attached to a hose. Another symptom is that there is a lot of air coming into the pool from the two inlets (more from the farthest inlet from the pump). One possibility is that ash from recent forest fires accumulated on the panels; the panels were hosed off (from ground level, it is a one-story house), but maybe this wasn't sufficient.Questions: Where could the air coming from? Could the year-old cartridge be the problem and need replacing? What is the best way to clean cartridges? Any and all suggestions will be appreciated.
Thanks,
Robert

Re: Solar heating not working as well as before

Hi, Robert,

Welcome to the forum

Air in the system is almost always a suction side leak.....somewhere between the skimmers and your pump impellor. That would also explain your lack of solar. It would not be the filter as that would be a pressure side leak and water would leak from the filter.

Re: Solar heating not working as well as before

When the solar was replaced, they may have added a relief valve to let the panels drain-down when not in use. This will pump a lot of air from the panels back through the returns until the panels are primed (It should stop after a few minutes though).

As for the temps -- I my water So-Cal) starts these days at 80 in the morning and will heat up to 85 by afternoon with solar. (Might have been 83 w/o solar). But I have other solar issues I won't go into now.

Re: Solar heating not working as well as before

FWIW, our solar panels are plumbed in parallel(getting about 10 GPM each) and even on a full sun day the water only comes out 2-4* warmer then it went into the panels. With that said, our pool will still gain 8-10* a day. You can check the temp of the heated water coming out by holding a pool thermometer in front of one of the returns. Also, like others have said you will see air bubbles coming back into the pool for a few min. upon start-up if you have a vacuum breaker.

BTW, when I first read that they were working fine not to long ago and then they just stopped working well, the first thing I thought was, "Maybe there is something covering the panels." I would get on a ladder and go up on the roof and look at the panels to make sure they are clean.

Re: Solar heating not working as well as before

Thanks! Those are a lot of excellent answers. The status now is no air bubbles! There is a two-way valve that sends the water from the pump either to the solar panels or bypasses them. With the pump off my wife turned the valve to see if she could hear the water draining back (there is a relief valve at the top of the panels) and then turned it back. No bubbles after that. Perhaps the two-way valve has an intermittent leak? At my wife's suggestion (you can tell who is in charge here ), I changed the filter cartridge to a brand new one. It has been cooler so there is no definitive conclusion on any improvement in the heating efficiency. The panels are clean (except maybe a residue of forest-fire ash after being hosed off). One other item, the float valve thing in the skimmer pops out of place every time the pump comes on. I think this is supposed to keep the pump from sucking air when the pool water is too low (we now have an auto pool filler). This started sometime during the summer. Should this be replaced? (it is as old as the pool- 34 years - and is about the only thing that hasn't been replaced.